Were I you, I would base my wheels around DT Swiss rims or Mavic and use XT hubs. Use double butted spokes as they will flex slightly and not break as a straight gauge spoke will. I have a CrossCheck built with DT Swiss rims and the XT hub using the double butted spokes and they have never even needed to be trued and I weigh 280lbs plus my gear. I have ridden thousands of miles on this set-up with no problems. They were handbuilt which probably lends to them being a great wheelset. Use XT drivetrain if possible, cranks and all. It will be robust and give you the gearing to climb with a heavy load.